There are approximately 84,500 to 114,000 new lower-limb amputations each year in the U.S. Amputation rates are rising each year, in part because of the rapid increase in diabetes and also because of an improvement in treating traumatic injury and vascular disease. More of the patients experiencing these problems are able to live longer but require a limb amputation to survive. Further, the recent wars in Iraq and Afghanistan have caused an increase in the number of servicemen and women who undergo an amputation, typically young individuals who are otherwise healthy. Because of the early age at which the amputation occurred, these individuals will be prosthesis users for many years. Thus, there is a strong need to create quality prosthetic limbs for the increasing lower-limb amputee population.
The design of an effective prosthetic socket is crucial to the rehabilitation and overall health of a person with an amputated limb. This point cannot be overemphasized. Most of the time and energy a practitioner applies in making a prosthesis is spent on fabricating the socket that must be fitted to the residual limb. The prosthetic socket must be shaped so that it supports the residual limb in load tolerant areas, while avoiding irritation of sensitive regions on the limb that contact the inner surface of the socket. If these criteria are not achieved, when the patient uses the prosthesis, residual limb soft tissue breakdown often occurs. The result is painful sores, blisters, ulcers, or cysts on the residual limb that typically restrict continued prosthesis use, and in severe cases, necessitate a further amputation to a higher anatomical level, which can lead to further disability. The incidence of skin breakdown in lower-limb amputees has been reported to be from 24% to 41%. Accordingly, at any one time, as many as 41% of prosthesis users may be experiencing breakdown of the tissue on the residual limb. The principle cause of such breakdown is a poorly fitting prosthetic socket.
Practitioners face challenges in making quality sockets for the increasing amputee population. Also, there is a shortage of prosthetists in the industry, and that shortage is expected to increase in the future, as the demand for prosthetic devices increases. A prosthetist's time is precious and must be used as efficiently as possible. It will therefore be evident that there is a need for technology to improve a prosthetist's efficiency, speed, documentation, repeatability, and quality of fitting a socket to a patient's residual limb, and to ensure a proper socket design early in the process of fitting a prosthetic socket to a recipient.
Modern prostheses are often made using computer-aided-design and computer-aided-manufacturing (CAD/CAM) methods, which were introduced to the prosthetics field about 25 years ago to address these needs. When using a CAD/CAM approach to produce a fitted socket, a practitioner measures the shape of the residual limb using either a cast impression or a commercially-available scanning device that implements one of a number of shape acquisition modalities (e.g., use of a laser scanner, contact hand digitizer, video scanner, structured light projection, or digitization of a plaster cast). The practitioner then designs a socket on a computer using one of several commercially available software packages. As shown in FIG. 1A, a design 22 can be viewed on a monitor 20 and modified as desired using input provided via a keyboard 24 or a mouse or other pointing device 22. As shown in FIG. 1B, the resulting shape is then sent electronically to a custom computer numerical control (CNC) mill 32, referred to in the art as a “carver,” to fabricate a positive model 34 as a block of material used for the model is rotated on an indexing table 30. This positive model is used to form the socket. For example, a thermoformer can be used to vacuum form a socket by heating a polymer cone and then vacuum forming it onto the positive model. Alternatively, a thermoplastic sheet 40 can be draped or wrapped over the positive model, as shown in a FIG. 1C. After the edges are trimmed, a completed socket 50 is provided, as shown in FIG. 1D.
Other methods for socket fabrication exist, including a novel motion guided extrusion technique (referred to as SQUIRT SHAPE™, developed at Northwestern University), and other rapid prototyping techniques. However, regardless of the method used for fabricating a socket, there is often a quality control problem that arises in the fabrication process, and means are needed to enable a prosthetic socket designer to determine if the fabricated socket indeed accurately matches the shape that was designed. Currently, practitioners creating sockets often spend too much time fixing or remaking the sockets that were produced incorrectly by the CAD/CAM process—where the errors typically arise either during the carving process or the forming process, or both. The benefits of CAD/CAM, which include improved efficiency, speed, documentation, and lower expense, are substantially reduced or even lost because of this problem. Prosthetists who have an in-office CAD/CAM system suite, central fabrication facilities, and manufacturers of CAD/CAM equipment used to produce sockets could thus clearly benefit from a new technology for evaluating the quality of each socket produced, to avoid the expense and delay incurred to fix or remake a socket as necessary to achieve a proper fit with the patient's residual limb.
For example, after making a socket, it would be desirable for a prosthetist to be able to place the socket in a device that can assess its shape and compare it with an electronic data file for the socket that was created using a CAD/CAM system. Such files define a desired shape for the socket and are stored on a computer hard drive and used for carving the socket positive model. The shape quality information relating to the match between the socket and the design file could then be presented to the prosthetist on the computer, using charts and images. The device might then indicate very clearly where modification is needed if the socket is not properly shaped. The practitioner could decide if the socket is acceptable, if it should be modified, or if a new socket should be made—all before attempting to fit the socket to the patient's residual limb. Having such information would potentially save a tremendous amount of time when fabricating sockets using a CAD/CAM system, by avoiding the need to bring the patient back to test fit a socket, determining that a problem exists, making adjustments, and then having the patient come in once again to repeat the process. Thus, such a device and system might save time and money and reduce pain to the patient.
A system to provide this functionality would require both hardware and software. The hardware would enable very precise shape measurements of the interior of a socket, for example, by using a contact stylus to measure the shape of the socket. The design for a related prior art measurement device was described in a 2003 publication. However, this early measurement device had several problems. Specifically, it was unable to measure areas of the socket with very high curvature. It was also clear that a refinement of the shape reconstruction algorithm was needed so that splines defining the shape of a socket interior might be assembled in r-z planes, rather than r-θ planes, or better, defined as a three-dimensional (3-D) shape. The earlier device also exhibited unacceptable errors and was sensitive to the position of the socket in the device, so that a slight axial misalignment of the measuring device relative to a socket's longitudinal central axis caused an unacceptable error in the evaluation of the socket.
There are a number of other benefits of being able to accurately assess a socket besides simply determining if the socket will properly fit the residual limb of the patient. For example, the data derived from this novel approach and the system that enables it could make it easier to evaluate the changes in a patient's socket design over time, e.g., by comparing a new socket with an old socket, to facilitate patient treatment and creation of a new socket design for the patient. This tool should enable the creation of a database and standards that facilitate substantial improvements in the CAM socket fabrication process. Another application of the tool would be to evaluate different manufacturing equipment and fabricators that are used to produce sockets, evaluate health service providers, and provide information usable by insurance companies.
It would also be desirable to employ such socket measurement hardware and software to determine if the CAD/CAM shaping of the positive model by carving and/or the forming of the socket over the positive model by a socket production facility produces sockets having errors of a consistent nature. By using the hardware and software discussed above to evaluate a plurality of different sockets that have been fabricated by a specific prosthetic facility using CAD/CAM, it should be possible to create an “inverse model” indicating corrections that should be applied by the facility to produce sockets much more closely achieving a desired design and having fewer errors. The corrections would be applied to the desired design file before carving the positive model to ensure that the resulting finished prosthetic socket actually matches the desired design and thus properly fits the residual limb of a patient as intended.
Accordingly, a new approach is needed that addresses these issues by providing an appropriate hardware and software tool or system for assessing the fit of a socket relative to: (a) an electronic shape file for a socket; (b) the shape of another prosthetic socket; (c) the shape of a positive mold of a socket; or, (d) a residual limb shape (e.g., acquired by imaging, contact sensing, or digitizing a cast). This tool should be useful in assessing the fit of sockets produced for both legs and arms, for othoses (i.e., devices that support rather replacing body parts, such as spine orthoses, limb and foot orthoses, and shoe inserts), and for other related tasks.